Rename DebugAction to tracing::Action and move related code from lib/Support to lib...

Rename DebugAction to tracing::Action and move related code from lib/Support to lib/IR and lib/Debug

This is a preparation for adding support for more infrastructure around the concept
of Action and make tracing Action more of a first class concept.
The doc will be updated later in a subsequent revision after the changes are
completed.

Action belongs to IR because of circular dependency: Actions are dispatched through
the MLIRContext but Action will learn to encapsulate IR construct.

Differential Revision: https://reviews.llvm.org/D144809